Storage area networks, also known as SANs, facilitate sharing of storage devices with one or more different host server computer systems and applications. Fibre channel switches (FCSs) can connect host servers with storage devices creating a high speed switching fabric. Requests to access data pass over this switching fabric and onto the correct storage devices through logic built into the FCS devices. Host servers connected to the switching fabric can quickly and efficiently share blocks of data stored on the various storage devices connected to the switching fabric.
Storage devices can share their storage resources over the switching fabric using several different techniques. For example, storage resources can be shared using storage controllers that perform storage virtualization. This technique can make one or more physical storage devices, such as disks, which comprise a number of logical units (sometimes referred to as “physical LUNs”) appear as a single virtual logical unit or multiple virtual logical units, also known as VLUNs. By hiding the details of the numerous physical storage devices, a storage virtualization system having one or more such controllers advantageously simplifies storage management between a host and the storage devices. In particular, the technique enables centralized management and maintenance of the storage devices without involvement from the host server.
In many instances it is advantageous to place the storage virtualization controller(s) in the middle of the fabric, with the host servers and controllers arranged at the outer edges of the fabric. Such an arrangement is generally referred to as a symmetric, in-band, or in-the-data-path configuration. Since such a storage virtualization system is integral to the operation of the storage area network, the unavailability or failure of part or all of a storage virtualization controller can be problematic, resulting in an inability of a host server to communicate with a storage device associated with its VLUN.
For these and other reasons, there is a need for the present invention.